In the production of seamless tubing, the tubular workpieces, referred to as shells, typically are passed through a plug mill, in order to reduce the wall thickness of the shell, as well as its outside diameter. Typically, the pierced shell, in a red hot condition, is advanced into the plug mill rolls, at which point it is picked up and driven by the mill rolls over a sizing mandrel plug. As the tubular shell passes through and is discharged from the mill rolls, the mandrel plug, which is now extremely hot, is removed from the mandrel, the mill rolls are opened slightly, and the shell is driven backwards through the mill in a non-working pass. As soon as the shell is upstream of the mill rolls, a new mandrel plug is brought into working position, and the shell, having been rotated 90.degree., is again advanced into the mill for a second working pass. Typically, the plug mill cycle consists of two passes, after which the shell is removed for further processing. In almost all cases, it is the practice to remove and replace the mandrel plug after each working pass through the mill, so that the just-used plug can be cooled before it is used in a subsequent operation.
Originally, the changing the mandrel plugs was performed manually, and this is still the case in many of the existing plug mills of earlier design. As will be appreciated, however, because the tube shells are being processed in a red hot condition, and because the mandrel plugs are extremely hot after use and they are often very heavy, the task of a mandrel plug changer is both difficult and dangerous. As a result, it is been proposed heretofore to employ mechanical mechanisms for replacement and removal of mandrel plugs. In general, prior mechanisms for this purpose have been limited in one or more ways, such as mechanical impracticability in the very severe environment of a plug mill, excessively long cycle time, or the like.
In accordance with the present invention, a new and improved plug changer is provided, particularly for a plug mill, which is mechanically simplified and rugged, yet which permits a plug change cycle to be completed in an extremely short time. The system of the invention incorporates a rotatable drum for the containment of a plurality of mandrel plugs, a feature which in itself is known. However, in conjunction with a rotatable drum, novel and improved arrangements are provided for supplying mandrel plugs to and from the drum and to and from working positions in the bite of the mill rolls.
In accordance with one of the more specific aspects of the invention, a pivoting, trough-like plug support is provided in conjunction with the plug holding drum, which is movable between inclined and horizontal working positions. In its inclined position, the trough-like support is arranged to receive a just-used mandrel plug as it falls by gravity from its working position in the mill, and to guide the used plug into a vacant pocket in the holding drum. In addition, in its inclined position, the trough-like support is arranged to receive a new plug from the holding drum. In its horizontal position, the trough-like support holds the plug in alignment with the tubular shell, advancing toward the mill rolls, such that the plug is picked up by the advancing shell and driven by the shell into working position. As it is moved from its inclined to its horizontal position, the trough-like support serves as an elevator, carrying the new mandrel plug upwardly into a ready position on the pass line of the mill.
In accordance with another and more specific feature of the invention, improved arrangements are provided for mounting and securing the trough-like support, described above, which, on the one hand, enables the discharge end of the support to extend as far as practicable into the bite of the mill, while at the same time easily accommodating removal and replacement of the mill rolls, as is required frequently when readying the mill for a new size of tube. To this end, provisions are made for displacement of the trough-like support independently of its normal pivoting motion, enabling the support to be quickly and easily displaced out of the way of the mill rolls without requiring any part of the plug feeding mechanism to be dismantled and removed.
In accordance with a further aspect of the invention, an improved arrangement is provided for pushing a new plug out of its pocket in the holding drum and onto the inclined supporting trough. Since the pushed-out mandrel plug will tend to slide by gravity down the inclined support trough, it is held in position by the pusher until the support trough is pivoted upward to elevate the plug into its ready position. For this purpose, the pusher mechanism incorporates a pivoted abutment plate, which engages the lower end of the mandrel plug and serves to guide and displace the plug during upward pivoting movement of the support trough. When the pusher mechanism is retracted, the abutment member assumes a new position, at a different angle, and serves, in effect, as a bottom wall for the active pocket of the holding drum.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment, and to the accompanying drawings.